Method for producing single microlenses or an array of microlenses

ABSTRACT

Disclosed is a method for producing single microlenses or an arrays of microlenses composed of a glass-type material, in which method a first substrate is provided with a surface containing impressions over which a second substrate composed of a glass-type material is placed at least partially overlapping it and is joined therewith under vacuum conditions. The substrate composite is tempered in such a manner that the second substrate softens and flows into the impressions of the first substrate, thereby structuring the side of the second substrate facing away from the first substrate in order to form at least one microlens surface.

This application claims priority under 35 U.S.C. §119 to GermanApplication No. 103 13 889.7, filed Mar. 27, 2003, and under 35 U.S.C§371 to International Application No. PCT/EP2004/002993, filed Mar. 22,2004, the contents of which are incorporated herein by reference intheir entirety.

BACKGROUND

The present invention relates to a method for producing singlemicrolenses or an array of microlenses composed of a glass-typematerial. According to the method, a first substrate having a surfacecontaining impressions is provided, a second substrate composed of theglass-type material is placed over the first substrate at leastpartially overlapping it and is joined with the same under vacuumconditions, moreover the substrate composite is tempered in such amanner that the second substrate softens and flows into the impressionsin the first substrate thereby structuring the side of the secondsubstrate facing away from the first substrate to form at least onemicrolens surface.

Furthermore, an alternative method for producing single microlenses oran array of microlenses made of a glass-type material is described inwhich a first substrate having a surface containing impressions, asecond substrate composed of the glass-type material is placed over thefirst substrate at least partially overlapping it and is joined with thesame, with a gaseous medium being enclosed in the impressions betweenthe first substrate and the second substrate and the substrate compositebeing tempered in such a manner that the second substrate softens andthe expanding gaseous medium is displaced in the region of theimpressions, thereby structuring the side of the second substrate facingaway from the first substrate to form at least one convex microlenssurface.

WO 01/38240 A1 describes a method for producing micromechanical and, inparticular, microoptical components composed of glass-type materialsusing technologies to structure semiconductor substrates in order toproduce functional elements made of glass in the micrometer andsubmicrometer range by means of glass-flow processes. In a first step,the impressions, which may be obtained by means of prior art standardlithography and etching methods, are placed in a preferably planesemiconductor surface. The prestructured semiconductor substrate is thenjoined with a plane substrate composed of a glass-type material, forexample by means of anodic bonding, and then heated above the softeningtemperature of the glass-type material. If a vacuum or low pressureprevails in the cavity enclosed by the respective impression in thesemiconductor material and the plane glass-type substrate, parts of thesoftened glass-type material are able to flow into the cavity. However,if a gaseous medium, for example air, is enclosed in the cavity inwhich, for example, the plane glass-type substrate is joined with thestructured semiconductor substrate under normal pressure conditions, thegaseous medium located in the cavity expands due to tempering anddisplaces the softened glass-type material located directly over thecavity.

In the first case, a concave shaped microlens structure forms inside thesurface of the glass substrate facing the semiconductor substrate. Onthe other hand, in the second case the local displacement leads to aconvex shaped microlens structure. In both cases the resulting curvatureof the microlens surface is dependent on the type and duration oftempering but, in particular, on the shape and size of the respectiveindividual impressions inside the semiconductor substrate. With the aidof the prior art method described in the preceding, spherically orelliptically symmetrical microlens surface can be produced.

U.S. Pat. No. 4,883,524 also describes with reference to FIG. 6 showntherein a glass-flow method which determines the shape of a binocularlens, in which local flowing off of the melted glass into a concaveimpression in the form of an ophthalmic lens of the optical near part ofa two-focal lens glass is producible.

SUMMARY

A method is disclosed for producing single microlenses or an array ofmicrolenses composed of a glass-type material in such a manner that thecurvature of the lens shape can be practically set as desired. Inparticular, it should be possible to produce single aspherical lenses orarrays of lenses in a cost-effective as possible manner.

The method according to the present invention is fundamentally based onthe technology of the glass-flow method described in WO 01/38240 A1 but,contrary to the prior art method technology for forming a microlenssurface, it does not use a single impression per microlens inside thesemiconductor substrate but rather provided are at least twoimpressions, the form, size and arrangement of which in relation to eachother determines the shaping process leading to forming the microlenssurface on the surface of the glass substrate facing away from thesemiconductor substrate and is distinguished by local materialdisplacements to create convex contours or by a controlled, selectivematerial flow into the at least two impressions, respectively cavities,provided in the first substrate to create concave or even convex surfacecontours.

In a first variant of the method, the first substrate composed of asemiconductor material, preferably present in the form of amonocrystalline silicon wafer and hereinafter referred to assemiconductor substrate, is provided with impressions placed in anotherwise plane upper side of the semiconductor substrate bysemiconductor technology means. The size, shape and arrangement of theimpressions is based on the desired curvature of the surface of theto-be-produced microlens surfaces as will be described hereinafter. Atleast two impressions are placed adjacent to each other in the upperside of the semiconductor substrate in such a manner that theimpressions remain separated from each other by means of a narrowintermediate fillet, the width of the intermediate fillet being usuallydimensioned much smaller than the smallest lateral dimension inside thetwo adjacent impressions.

The prestructured semiconductor substrate is intimately joined with thesecond glass-type substrate, hereinafter referred to as glass substrate,under vacuum conditions preferably by means of anodic bonding in such amanner that the glass substrate closes the impressions gas tight to formcavities in which vacuum conditions prevail.

In the following, the substrate composite undergoes a tempering processin which the glass-type material softens and flows locally into thecavities due to the vacuum conditions prevailing in the cavities untilthe cavities are preferably completely filled with the softenedglass-type material.

Providing the size, shape and arrangement of the impressions inside thesemiconductor substrate permits preselecting exactly the amount ofglass-type material that flows into the cavities formed by theimpressions. Due to suited selection of the width of the glass substratedependent on the prescribed geometry, the material flow directed intothe cavities on surface of the semiconductor substrate facing thesemiconductor substrate leads to local sinking of the surface occurringin the region in projection over the cavities. The local sinking of thesurface ultimately represents a concave surface contour, the localcurvature, size and shape of which determines the optically effectivesurface of a microlens.

Corresponding combination of suitably formed impressions, respectivelycavities, and suitably arranged on the surface of the semiconductorsubstrate with suited selection of thickness of the glass substratepermits reproducible production of microlenses having a definedcurvature of the surface, in particular the production of asphericalsingle lenses, respectively arrays of lenses, using simple technicalmeans which moreover can be realized cost-effectively.

Following the aforedescribed shaping procedure, after cooling of theglass substrate, the semiconductor substrate is separated from the glasssubstrate and single microlenses or whole arrays of microlenses areobtained by means of polishing, grinding, sawing or similar processes.The separation as such can be simplified by previously providing aseparation layer between the semiconductor substrate and the glasssubstrate, for example by providing a metal, graphite or similarseparation layer. The simplest method of separation of the semiconductorand the glass substrate is, however, still dissolving the semiconductorsubstrate itself wet-chemically.

The invented method does not only permit, as described in the preceding,production of concave microlens surfaces, but also the formation ofconvex microlens surfaces, for which two fundamentally differentalternative method variants are at disposal, which differ essentially inwhether vacuum pressure conditions or normal pressure conditions prevailin the cavities before tempering.

If, as described in the preceding, joining the semiconductor substratewith the glass substrate is conducted under vacuum conditions, at leasttwo impressions, respectively cavities, which are separated by aso-called intermediate fillet area have to be placed in thesemiconductor substrate surface. The intermediate fillet area rises likea stamp or a island between the at least two impressions, which arearranged separated from each other or can be constructed in such amanner that they completely enclose the intermediate fillet area in theform of a through-going “trough”. The lateral extension of theintermediate fillet area is many times larger than the aforedescribedintermediate fillet. A more exact idea of the arrangement of theintermediate fillet area relative to the adjacent impressions isdescribed, in particular, in the following preferred embodiments.

As a result of anodic boning such a type prestructured semiconductorsubstrate with a glass substrate and subsequently tempering above thesoftening temperature of the glass-type material, the softenedglass-type material over the intermediate fillet area begins to flowinto the provided adjacent impressions, thereby yielding a convexsurface contour over the intermediate fillet area on the glass-substratesurface facing away from the semiconductor substrate. The curvaturebehavior of the convex form and its shape and size can be exactlyprescribed by the shape, size and arrangement of the impressions aboutthe corresponding intermediate fillet area and its dimensions. Furtherdetails on this described variant of the method are determined in thefurther description with reference to the preferred embodiment.

The second alternative of the method for producing convex lens surfacesprovides joining the semiconductor substrate with the glass substrateunder normal pressure conditions in such a manner that a gaseous medium,for example air, which expands upon heating is enclosed in the cavitiesprovided by the impressions. The temperature-dependent expansion of thegaseous medium inside the cavities displaces locally the softened glassmaterial directly over the cavities in such a manner that convex bulgesare yielded on the surface of the glass substrate facing away from thesemiconductor substrate. The curvature of the bulges can be prescribed,in the same manner, by the shape, size and arrangement of thecavities/impressions placed on the semiconductor substrate.

In addition to being able to determine the surface curvature forming onthe upper side of the glass substrate facing away from the semiconductorsubstrate by means of the aforedescribed shaping process, the shape,size and arrangement of the impressions, respectively cavities, insidethe semiconductor substrate can also determine the lateral extension andthe peripheral contour of the microlens forming on the upper side of theglass substrate.

Independent of the variant of the method for producing convex or concavesurface contours described in the preceding it is especiallyadvantageous for precise delimiting, respectively setting, of theperipheral edge is placing a additional semiconductor substrate, whichprovides recesses, preferably in the form of openings, adapted accordingto the desired peripheral geometry of the to-be-produced microlenses onthe upper side of the glass substrate facing away from the structuredsemiconductor substrate. The openings inside the additionalsemiconductor substrate are aligned to lie opposite according to thearrangement of the impressions in the first semiconductor substratebefore the second semiconductor substrate is joined with the surface ofthe glass substrate by means of anodic bonding. The otherwise flatjoining of the glass substrate and the additional semiconductorsubstrate is also retained during the tempering, which leads tosoftening the glass substrate.

In the case of a convex as well as of a concave forming microlenssurface, the linear nature of the delimiting edge circumventing themicrolens surface, which is determined by the opening in the additionalsemiconductor substrate, is not influenced, thereby permitting precisedetermination of the peripheral edge of the forming microlens.

As mentioned in the preceding, the invented method permits producingmicrolenses with almost any desired curved lens surfaces, preferablyaspherical lens surfaces with dimensions ranging from a few micrometersup to 1 mm and more. Such type lenses can have almost any desiredperipheral contour, preferably circular or rectangular lens shapes.

In addition to producing single microlenses, the invented method,however, is also suited for producing array-like arranged lenses, asthey are used, in particular, in microsystem technology, for example,for optical imaging on CCD array arrangements.

After completion of the aforedescribed tempering and the followingcorresponding cooling for solidifying the glass substrate, thesemiconductor substrates can be removed, for example by means of as suchknown etching, from both sides of the surfaces of the glass substrate.Alternative technologies, such as for example, grinding off can also beemployed. In particular, the aim is to separate the substrate with theglass-filled impressions from the glass substrate to create a planesurface. Depending on the use, the microlenses, respectively the arraysof microlenses, produced by means of the aforedescribed manner can bedetached or selected in an array-like arrangement by means of cutting orgrinding processes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the following using preferredembodiments with reference to the accompanying drawings without theintention of limiting the scope or spirit of the overall inventive idea.Depicted is in:

FIG. 1 process steps for producing a concave shaped microlens,

FIGS. 2 a,b a three-dimensional representation for structuring suitedsemiconductor substrates for producing a convex round lens (a) and acylindrical rectangular lens (b),

FIG. 3 a variant of the method according to FIG. 1,

FIGS. 4 a,b process steps for producing a convex shaped microlens,

FIG. 5 a three-dimensional representation of a layer arrangement forproducing a convex shaped microlens,

FIG. 6 a process step representation for producing a convex shapedmicrolens by means of material displacement and

FIG. 7 a variant of the method for producing a convex shaped microlensfor the process step according to FIG. 4.

DETAILED DESCRIPTION

FIG. 1 shows six process steps with which a microlens with a concavelens surface can be produced. In a first process step the aim is toprovide a base substrate composed of a semiconductor material, whichpreferably comprises a monocrystalline silicon and is referred tohereinafter as silicon wafer 1, having structures in the form ofimpressions 1, which can be placed in the surface of the silicon wafer1, for example by means of an etching process, such as dry etching. Asdescribed in detail in the following, the shape, size and arrangement ofthe impressions 1 is of decisive significance for the ultimately formingsurface curvature and shape of the microlens. The impressions 1 placedin the surface of the silicon wafer 1 according to the preferredembodiment of FIG. 1 have a wide central impression adjacent to eachside of which are additional impressions at increasingly smaller lateraldistances. Each single impression is delimited from the adjacentimpression by a narrow intermediate fillet 2. Depending on theto-be-produced curvature of the lens surface, the shape, size, andarrangement of the single impressions 1 can deviate from the impressionsshown in FIG. 1.

In the subsequent process step, the surface 3 of silicon wafer 1provided with the impressions 1 is joined with a substrate composed of aglass-type material, for example a glass wafer 4 composed of pyrex glassor borofloat glass under vacuum conditions by means of anodic bonding.Alternative joining techniques, such as for example gluing techniques,can of course also be utilized to join the glass wafer 4 with thesilicon wafer 1 if the used joining technique is able to withstand therequired high process temperatures.

The upper side 5 of glass wafer 4 facing away from the silicon wafer 1is joined with another silicon wafer 2, preferably also utilizing anodicbonding, with the silicon wafer 2 having a recess 6, the shape and sizeof which is matched to the arrangement of the impressions 1 inside thesilicon wafer 1 and is aligned correspondingly opposite it on the upperside 5 of the glass wafer 4.

In a subsequent tempering process, which is shown in process step 4, theglass-type material of the glass wafer 4 softens and flows into thecavities determined by the impressions 1 and fills them completely asindicated in the process step 4. The flow process of the softenedglass-type material into the cavities determined by the impressions 1 issupported by the vacuum prevailing in the cavities. The shape, size andarrangement of the cavities in the silicon wafer 1 can selectively setthe amount of glass that flows into the cavities. With correspondingselection of the thickness of the glass wafer 4, due to theaforedescribed flowing of the glass-type material into the cavities, alocal sinking of material occurs, developing exactly inside the opening6 of the silicon wafer 2. The linear delimiting edge 7 determined by theopening 6 in the silicon wafer 2 determines the geometry of thedeveloping microlens, whose surface is formed by the sinking of thesoftened glass-type material and is described in process step 4according to FIG. 1.

In addition to the vacuum enclosed inside the cavities, the materialsinking in the softened glass-type material can be supported bytempering conducted under normal conditions, preferably 1 bar, in such amanner that the cavities determined by the impressions 1 are completelyfilled with the corresponding softened glass material. In this manner,the whole volume of the glass material that flowed into the cavities isexactly predetermined by the volume prescribed by the impressions 1 inorder to ultimately obtain a certain curvature on the upper side 5 ofthe glass substrate 4 by means of the material sinking. However, thecavities defined by the impressions 1 must not exceed a maximum size,respectively expansion, with the geometry and the arrangement of theimpressions ultimately being dependent on the selected thickness of theglass wafer 4. Thus, the form of the impressions 1, the selectedthickness and density of the glass material of glass wafer 4 and theselected tempering conditions determine the different flow behavior andthe resulting curvatures and shapes on the glass surface 5 of the glasswafer 4.

Following the shaping of the glass material by means of tempering andits subsequent cooling, the silicon wafers 1 and 2 are removed from theglass substrate 4. In the simplest case, this occurs by means ofwet-chemical etching. Finally, the bottom side of the glass wafer has tobe leveled, for example by means of grinding and subsequent polishing ofthe surface. See process steps 5 and 6 in FIG. 1.

Corresponding separation layers can also be provided between thesurfaces of the glass substrate 4 and the silicon wafers 1 and 2, forexample metals that melt at low temperatures or a graphite layer, thuseven permitting separating the silicon wafers from the surfaces of theglass substrate 4 without the conventional etching techniques.

The method presented with reference to FIG. 1 permits producingmicrolenses having defined concave shaped surface curvatures with a veryhigh degree of reproducibility.

To produce arrays of lenses distributed over an area, the silicon wafer1 has to be prestructured array-like with the respective impressions 1required for forming the desired microlenses. The process steps forproducing suited arrays of lenses following suited prestructuringcorrespond to the process steps 2 to 6 according to the aforedescribedFIG. 1.

FIGS. 2 a and b show a three-dimensional representation of the layerstructure, which fundamentally corresponds to the process coursedepicted in FIG. 1. To produce a round microlens, FIG. 2 a shows asilicon wafer 1 whose surface is provided with a multiplicity ofsymmetrically arranged sexagonal prismatic impressions 1. Arranged in aring around a central, largest sexagonal impression, are a multiplicityof smaller sexagonal impressions which for their part are also dependingon the curvature behavior of the to-be-produced microlenses, impressionsof various shapes, geometries and arrangements can be selected, thus thestructured silicon wafer 1 shown in FIG. 2 a is only a concrete caseexample. Provided over the prestructured silicon wafer 1 is a glasswafer 4 over which for its part is shown a silicon wafer 2 provided withan opening 6. The opening 6 defines the circular edge of the microlenssurface yielded by means of tempering as described in the preceding, inparticular, with reference to FIG. 1 process step 4.

Furthermore, the invented method also permits producing microlenses witha peripheral boundary which deviates from a circle, such as for exampleis the case with cylindrical lenses. For this purpose, the silicon wafer1 shown in FIG. 2 b is provided with a multiplicity ofrectangular-shaped impressions 1 arranged side by side and separated byintermediate fillets in the manner shown in FIG. 2 b. Adapted to theoverall basic form prescribed by the structured wafer 1, the siliconwafer 2 is provided with a corresponding rectangular opening which forits part determines the delimiting edge of the microlens surface formingby means of tempering.

The structuring possibilities of the substrate surface of the siliconwafer 1 shown in FIGS. 2 a and 2 b are only representative case examplesfor forming circular or rectangular-shaped microlenses and fundamentallypermit concluding that with the aid of the invented method microlensesof practically any desired shape can be produced.

FIG. 3 shows a variant of the method for the process step shown in FIG.1 process step 4. In contrast to FIG. 1, the cavities represented by theimpressions 1 are only partially filled with softened material. Such atype variant of the method is suited, in particular, in cases in whichthe tempering is monitored by a time-dependent tempering control therebyenabling monitoring and correspondingly setting the curvature behaviorof the lens surface developing locally at the surface 6 of the glasssubstrate 4.

The process situation described in the preceding figures permitsproducing concave curved microlens surfaces. For producing convexmicrolens surfaces, there are fundamentally two methods available, ofwhich the first is described in FIGS. 4 and 5 and the second in FIG. 6.

FIG. 4 a shows a cross section of a joining structure comprising thesilicon wafer 1, the glass substrate 4 and the silicon wafer 2. Ofdecisive significance for the further process steps is the structuringof the silicon wafer 1, i.e. the arrangement of the impressions 1 on thesurface of the silicon wafer 1 into which, during the followingtempering process, the softened glass-type material flows to form asingle convex microlens surface. The structured silicon wafer 1 isprovided with a intermediate fillet area 8 which is bordered on bothsides directly adjoining by a number of impressions 1. The singleimpressions are each separated from each other by intermediate fillets 2whose lateral dimensions are much smaller than the lateral extension ofthe intermediate fillet area 8. In the shown example, directly adjoiningthe intermediate fillet area 8 on both sides are in three cavities K1,K2, and K3, respectively, determined by the impressions, with thecavities K3 having the largest lateral width and therefore offer thelargest volume for receiving the glass-type material, which in asoftened state is flowable. The layer buildup depicted in FIG. 4 is alsosubjected to the process step 2 in FIG. 1 in such a manner that joiningbetween the glass substrate and the silicon wafer 1 was conducted undervacuum conditions in such a manner that vacuum conditions prevail in thecavities K1, K2, K3. A sealing edge 9 surrounding the cavities K3 onboth sides ensures that vacuum conditions are maintained in the cavitiesK3 during the tempering process.

The opening 6 placed in silicon wafer 2 is preferably positionedsymmetrically over the intermediate fillet area 8 in such a manner thatin projection, the delimiting edge 7 determined by the opening 6 liesover the cavities of the silicon wafer 1.

FIG. 4 b shows the outcome of the substrate layer buildup following thetempering process, in which the cavities K1-K3 are completely filledwith the glass-type material. Moreover, the silicon wafer 2 has sunk inrelation to the silicon wafer 1 as a consequence of the material flowinto the cavities, with a convex shaped surface contour forming in thearea of the opening 6 as the microlens surface, which ultimately occursdue to the selective provision of the intermediate fillet area 8arranged in the center in relation to the opening 6, which preventssinking of the softened glass-type material. But rather a lateralflowing off of the softened glass-type material into the cavities K1-K3occurs, which are disposed adjacent to the intermediate fillet area 8.

FIG. 5 shows a three-dimensional representation of the wafer requiredfor successfully conducting the aforedescribed method for producingconvex microlens surfaces. The silicon wafer 1 is provided with asurrounding fillet-like border 9, which as described in FIG. 4, servesto maintain the vacuum conditions. Provided within the surroundingborder 9 are differently dimensioned intermediate fillet areas 8 servingin their entirety to form a convex microlens surface. In the shownpreferred embodiment, the differently dimensioned intermediate filletareas 8 rise stamp-like or island-like from the bottom of the impressionenclosed by the border 9. In FIG. 5, the impression is basically a largearea rectangular recess in the surface of the silicon wafer 1, which issurrounded by the border 9 and in whose interior single islands protrudeupward.

Glass wafer 4 is joined with the prestructured silicon wafer 1 undervacuum conditions by means of anodic bonding. Occurring in the samemanner is the close joining of the silicon wafer 2, provided with anopening 6, to the surface of the substrate 4, with the opening 6 beingdisposed in the center over the intermediate fillet areas 8 of thesilicon wafer 1.

The glass-type material of the glass substrate 4 softening by means ofthe tempering process flows into the intermediate areas formed by theintermediate fillet areas 8, thereby ultimately yielding inside theopening 6 at the surface 5 of the glass substrate 4 a convex-shapedsurface contour.

FIG. 6 describes another possible manner of forming convex microlenssurfaces. The point of departure is, as in the process step 1 withreference to FIG. 1, the provision of a prestructured silicon wafer 1having impressions 1 placed therein. In contrast to the method accordingto FIG. 1, the anodic bonding of the glass wafer 4 with the siliconwafer 1 does not occur under vacuum but under normal pressure conditionsso that the cavities K1, K2, K3 formed by the impressions 1 resulting inencapsulating gas, preferably in the form of air, which expands whenheated. In the subsequent tempering procedure, corresponding to FIG. 6,the glass-type material softens, with the air present in the cavitiesK1, K2, K3 expanding simultaneously, which leads to displacement asdepicted in FIG. 6. Depending on the size of the cavities, glass-typematerial over the cavities is displaced upward corresponding to the airportion to form a convex shaped lens surface. Depending on the selectionof the size and arrangement of the cavities K1,K2,K3 relative to theopening 6 of the silicon wafer 2, almost any desired shaped convex lenssurface curvatures can be created.

Finally FIG. 7 shows an alternative embodiment for forming the siliconwafer 2, which in contrast to the preceding embodiments, does notprovide a through-going opening 6 but just an impression 6′ whichtogether with the surface 5 of the glass substrate 4 encloses a volumespace. Certain pressure levels can be set inside the volume, for exampleto further influence the surface of the lens.

With the aid of the invented method, any desired aspherical lenssurfaces, be it convex or concave formed microlens surfaces, can bereproducibly fabricated. The described method variants permit realizingsimple to conduct process steps cost-effectively, thereby makingextremely cost-effective production of such type microlenses ormicrolens arrays possible.

Finally, it must be pointed out that the invented method can be utilizedjust as successfully for producing microlenses or microlens arrays madeof plastic polymers. The term glass-type material is to be understoodthat the material has a temperature at which the material softens, atwhich the material transcends into a viscous, flowing state.

In a particular further embodiment variant, the microlenses,respectively the microlens arrays, obtained with this method can beutilized as replication structures, respectively master molds, forfabricating microlenses, respectively microlens arrays, with exactpredetermined lens surfaces, for example within the scope of casting.Furthermore, the obtained lens surface contours can be transferred bymeans of galvanic casting to more robust matrix substrates, for exampleNi-matrixes, which serve for further replication of microlens forms.

LIST OF REFERENCES

-   1 impressions-   2 intermediate fillets-   3 surface of the silicon wafer-   4 glass substrate-   5 surface of the glass substrate-   6 opening-   7 delimiting edge-   8 intermediate fillet area-   9 surrounding border

1. A method for producing single microlenses or an array of microlensescomposed of glass, the method comprising: providing a first substratewith a surface containing impressions over which a second substratecomposed of glass is placed at least partially overlapping it and isjoined therewith under vacuum conditions, and pempering the substratecomposite in such a manner that the second substrate softens and flowsinto the impressions of the first substrate, thereby structuring theside of the second substrate facing away from the first substrate inorder to form at least one microlens surface, wherein for forming eachmicrolens surface, the softened glass of the second substrate flows intoat least two impressions of the first substrate, the shape, size, andarrangements of the two impressions determining the curvature of themicrolens surface.
 2. A method according to claim 1, wherein a firstsubstrate is provided containing a first impression into which saidsoftened glass flows during the tempering to form a concave surfacecontour at the microlens surface opposite the first substrate andwherein provided beside the first impression and separated by anintermediate fillet is a second impression into which an amount, whichis determinable, of the softened glass flows determined by the shape,size and arrangement of the second impression to form a prescribedcurvature of the microlens surface in at least a subdomain of theconcave surface contour.
 3. A method according to claim 1, wherein thefirst substrate contains at least two impressions separated by anintermediate fillet area over which a convex surface contour forms atthe microlens surface opposite the first substrate due to the lateralflowing off of the softened glass into the at least two impressionsduring the tempering.
 4. A method according to claim 1, wherein a metallayer is placed between the first and the second substrate.
 5. A methodaccording to claim 1, wherein the structured surface of the firstsubstrate is provided with impressions having structure widths B and thesecond substrate having a thickness D and wherein the following appliesapproximately:B<0.5*D.
 6. A method according to claim 1, wherein the first substrateis a semiconductor substrate and/or wherein the glass is a borosilicateglass.
 7. A method according to claim 1, wherein the first substrate isa semiconductor substrate and/or wherein the glass is a polymer-basedplastic material.
 8. A method according to claim 1, wherein joining ofthe first substrate with the second substrate composed of glass occursby anodic bonding or by a gluing method.
 9. A method according to claim1, wherein the tempering is conducted by controlling the temperature andthe duration to obtain a certain curvature of the forming microlenssurface.
 10. A method according to claim 1, wherein before thetempering, a third substrate is placed on the side of the secondsubstrate facing away from said first substrate, and wherein the thirdsubstrate is provided with at least one impression or at least oneopening having a delimiting contour, which delimits the peripheralcontour of the forming microlens.